Radio frequency identification (RFID) technology has become increasingly commonplace for use in inventory tracking, loss prevention, and other uses. An RFID system may include a transponder or tag that is placed on an object and an interrogator or reader that wirelessly receives information transmitted by the tag. RFID tags may be broadly classified as active tags that include a local power source such as a battery, or passive tags that are activated by electromagnetic waves generated by the reader that induce a current in an antenna within the tag.
RFID tags can include an electronic circuit that may be in the form of a chip or integrated circuit (IC). The chip may store data that is communicated to the reader. In contrast, a chipless RFID tag has neither an integrated circuit nor discrete active electronic components, and may be printed directly onto a substrate resulting in a lower cost than a chipped RFID tag.
A chipless RFID tag may include a receive antenna that intercepts interrogator output, a transmit antenna that broadcasts data that is received by the interrogator, and a plurality or array of resonators (i.e., a multiresonator) electrically coupled between the receive antenna and the transmit antenna. During use, the reader may output a broad band or spectrum of radio frequencies. Depending on the configuration of the multiresonator, one or more of the radio frequencies may include a frequency-dependent antenna load that is intercepted by the receive antenna and causes the multiresonator to resonate. The resonation modifies the signal that is transmitted by the transmit antenna and may be received by the interrogator. Each RFID tag may be encoded by etching a conductive film to result a specific set of patterned resonant structures that form the multiresonator. For unique identification of a particular tag from a set of tags, each transponder must be made to include a unique multiresonator design, which is an expensive process.
The receive antenna, the transmit antenna, and resonators may be prepared using one or more patterning techniques to pattern a conductive layer, for example a metal layer. Various patterning techniques may be used, for example, stamping, chemical etching, mechanical etching, laser etching, direct writing of a metal layer, vapor deposition, etc. In one technique, a foil master is etched away to create the final structure.
As a practical matter, RFID technology uses radio frequencies that have much better penetration characteristics to material than do optical signals, and will work under more hostile environmental conditions than bar code labels. Therefore, the RFID tags may be read through paint, water, dirt, dust, paper, human bodies, concrete, or through the tagged item itself. RFID tags may be used in managing inventory, automatic identification of cars on toll roads, security systems, electronic access cards, keyless entry and the like.
Thus, unless an RFID system is designed merely to detect the presence or absence of a tag, each RFID tag from a set of tags must include a different resonator configuration that is formed during manufacture. The resonator configuration is hardwired into the RFID tag, and thus the tag includes one resonator configuration during the entire lifetime of the tag.